The present invention relates to pressure or draw bars, in particular switch bars or coupling rods (draw bars) of high-voltage circuit-breakers, of fiber-reinforced insulating material with metallic fittings on the front faces thereof for pressure or force transmission, in which the fiber-reinforced insulating material contains fibers oriented parallel to the axis of the draw bar which are secured in recesses arranged between the fitting body and transversely to the bar axis with tying elements absorbing the forces and being impregnated with a curable synthetic material which is subsequently cured, and in which the fitting body has internal threads, into which a connecting element having external threads is screwed, which connecting element has at least one connecting aperture.
Such pressure or draw bars are known from E-A2-0 115 763. In these known bars the connecting element serving to introduce force consists of a simple threaded bolt with a connecting aperture, which is screwed into the internal threads of the fitting body and is height-adjusted by a nut resting against the front face of the fitting body. The bar itself consists of a core of rigid expanded plastics, on which several layers of insulating fibers of high tensile strength are applied axis-parallel or extending obliquely to the axis, which are impregnated with synthetic resins and cured. These fibers consist of at least one layer of axis-parallel fibers, which, before being cured, are secured in suitable manner on the external surface of the metallic fitting body, for example through tying into annular grooves, which are located on the outer surface of the fitting body. The given height-adjustability of the connecting aperture, obtained by screwing the connecting element into the fitting body to different depths is, however, relatively unstable, since the position--once it has been selected--is only secured by a nut, which can loosen through changing force transmissions and, furthermore, requires additional construction lengths.
Furthermore, from E-B1-0 087 384 it is known that for manufacturing such, in particular, hollow-cylindrical pressure or draw bars, that fibers oriented essentially parallel to the bar axis and conical fitting bodies, which have external screw-shaped recesses, in which the fibers are secured form-fittingly, can be used. The fibers in this arrangement are led to and from in layers and always secured in the recesses, for which a wire, a piece of cord or any other tying element, which absorbs tensile forces, is used, which is placed screw-shaped into the recesses. Subsequently, the pressure or draw bar is impregnated with a curable synthetic material and--after this step--curing takes place. In this way particularly good force transmission between the pressure or draw bar and the fitting bodies are obtained, because in this transmission it is primarily the fibers that participate, while the synthetic material, which penetrated during impregnation, during shaping and subsequently during curing is only indirectly involved.
Particularly advantageous is use of such pressure or draw bars known from E-B1-0 087 384 of electrically insulating synthetic materials as transmission elements in high-voltage circuit breakers, the switch sites of which standing at high-voltage potential are actuated by a drive connected to ground potential, because these permit particularly good securing of the fibers at the metallic fitting bodies serving as reinforcement of the insulating material.